Optical fiber offers higher bandwidth and faster data rates compared to copper cables. Optical fiber has traditionally been used in long-haul backbones of the Internet. Metro optical networks are also widely deployed for metropolitan-area networks. Recently, optical fiber networks are now reaching residential access networks that connect individual homes to a network carrier's central offices.
Different multiplexing techniques, for example, TDM or WDM, are used in optical networks to increase the capacity of the underlying optical fibers. A WDM optical network employs multiple wavelengths or a band of wavelengths for simultaneous data transmissions. A WDM optical network generally comprises a plurality of wavelength crossconnects (WXCs), also referred to as nodes. Each node is connected to one or more other nodes via optical links. Each node performs key functions such as wavelength multiplexing/demultiplexing, and switching. Each node may optionally perform wavelength conversion or optical/electrical/optical (OEO) conversion. If no wavelength conversion or optical/electrical/optical conversion is performed by a node connecting two adjacent optical links, the so-called wavelength continuity constraint applies to a spectrum resource allocated to carry data through these two adjacent optical links. The spectrum resource is required to be of the same wavelength and is available on both links.
In a WDM optical network without wavelength or OEO conversions, to transmit data from a source node to a destination node interconnected by multiple optical links, the network needs to configure a route between the two nodes and to assign a spectrum resource to accommodate the spectrum demand of the data transmission. The route would include various links that have the resource to support the spectrum demand. The algorithm used by the network to select a route and assign a spectrum is generally referred to as routing and spectrum assignment (RSA) algorithm.
In optical networks, one goal of RSA is to determine an optimal path between a source node and a destination node. An optimal path may be a path that is shortest in length, smallest in transmission delay, or lowest in cost, etc. Another goal of RSA is efficient use of spectrum resources. An ideal RSA scheme prevents spectrum fragmentation in which used and unused spectrum segments are interspersed. Spectrum fragmentation leads to wasted spectrum resources that are blocked and cannot be assigned. An ideal RSA scheme can achieve zero or low blocking ratio (the percentage of blocked spectrum in the band of frequencies).
However, a RSA algorithm that provides efficient use of spectrum resources is often computationally expensive. Also, as spectrum resources on optical fibers become scarce, it is critical to maximize their utilization by efficient provisioning strategies or allocation algorithms. There is a need for an advanced RSA algorithm that can achieve high spectrum efficiency with low computational complexities.